102 



PRODUCTS, ADVENTITIOUS. 



for this reason that chemical change is in 

 some measure worked out by (and, infer- 

 entially, that chemical differences exist ab 

 online in) blastemata themselves ; but, even 

 thus, the cells must have an influence second- 

 ary only in time, not in importance. Like ali 

 membranes placed between fluids of different 

 nature (the surrounding fluid and that con- 

 tained within them), the cell-wall must be the 

 seat of endosmosis and exosmosis, and the 

 chemical result must be regulated, on the part 

 of the cell, not only by the nature of mem- 

 brane or cell-wall to be permeated, but by the 

 nature of f he fluid contents of the cell. 



(r.) That the potential qualities of different 

 blastemata differ is perfectly obvious ; exist- 

 ences (such as cancer, pus, tubercle) must be 

 formed from materials endowed with different 

 vital tendencies. Concerning the nature and 

 essence of this potential difference nothing is 

 known with certainty. As respects the pro- 

 cess by which its own special character is 

 impressed on each blastema, and the locality 

 in which that process is accomplished, three 

 cases are possible : either the special character 

 is given while the elements of the blastema 

 are still circulating with the blood ; or while 

 those elements are undergoing filtration 

 through the walls of the vessels ; or at both 

 these periods. Now, though it is probable 

 that the filtration process exercises some in- 

 fluence of the kind under consideration, yet it 

 is next to certain that the main influence is 

 exercised on the blastemal elements within the 

 vessels by the constitutional .slate of the indi- 

 vidual, that upon this constitutional state, 

 and not upon any local process whatsoever, 

 mainly depends the issue of a blastema, 

 whether it shall be evolved, for instance, into 

 cancer or fibrous tumour, pigment-cells or pus, 

 fat or enchondroma. 



The blood being the source from which 

 blastema is derived, there are three distinct 

 situations in which it may, a priori, be sup- 

 posed to undergo evolution into structure : 

 (.) within the vessels : (b.) in the substance 

 of the vascular walls : (c.) outside the vessels. 

 Whether evolution does occur in all these 

 situations requires to be examined into. 



(a.) Certain adventitious formations are 

 unquestionably found occasionally in the in- 

 terior of the veins, and their presence can only 

 be accounted for in one of two ways, either as 

 the result of the absorption and subsequent 

 germination of certain elements of growths 

 pre-existing elsewhere, or of primary evolution 

 of blastema which had never escaped from the 

 vessels. There can be little doubt that in the 

 great majority of cases intra-venous Forma- 

 tions are produced by evolution of absorbed 

 elements; but it appears probable that they 

 may sometimes spring from retained or non- 

 exuded blastemal elements. It is true, the 

 embryonic production of a fragment of natural 

 tissue within the vessels is an anomaly of 

 nutrition of which no example has, as far as 

 we know, been witnessed ; analogy is conse- 

 quently opposed to the admission of a germi- 



nating force in non-exuded blastema. 



Jt is 



likewise true that, in respect of the simplest 

 form of blastema (the inflammatory) escape 

 from the vessels appears essential to evolu- 

 tion as a general fact ; nevertheless, it is to 

 be remembered, inflammation-products are 

 evolved within the vessels in cases of arteritis 

 and phlebitis, and in the healthy state epithe- 

 lium is constantly being produced on the 

 internal vascular surfaces. Hence the possi- 

 bility of retained blastema germinating within 

 the vessels must be, at least provisionally, 

 conceded ; and such germination may be 

 imagined most readily to occur where pecu- 

 liarities of texture interfere (as in structures 

 of the erectile class) with the process of 

 exudation.* 



(A.) Nodules of adventitious structure have 

 sometimes been met with in the actual sub- 

 stance of the parietes of the veins. The locali- 

 zation of these nodules becomes intelligible on 

 the supposition either that blastema, furnished 

 by the blood circulating in their interior, has 

 germinated during the process of filtration 

 through the vascular coats ; or that the blas- 

 tema was originally supplied by the vasa vaso- 

 rum. The fact that the nodules in question 

 have been principally met with in veins of a 

 certain size (where exudation does not habitu- 

 ally occur) makes it probable that, in some 

 cases at least, the vasa vasorum are the source 

 of supply. 



(c.) But both localities, so far considered, 

 are rare, though possible, seats of germination ; 

 hence it follows directly that the common site 

 of the phenomenon must be outside the 

 vessels, and indirectly that the process of 

 filtration through those tubes is commonly a 

 necessary element in the generation of a blas- 

 tema apt for evolution. Hence it is that 

 exudation fluid has been employed as a sy- 

 nonym of blastema in general. Now the 

 possible positions outside the vessels are : 

 the intervascular interstices of the various 

 tissues and organs ; the free (or sub-epithe- 

 lial) surfaces, mucous, serous, and cutaneous ; 

 the surface (and, mediately, by imbibition, 

 the substance) of the extra-vascular tissues ; 

 and, lastly, adventitious surfaces, produced by 

 wounds and other agencies. Now observa- 

 tion (while it has decided that germination 

 does actually occur in all of them) has proved 

 the first-named of these situations to be by 

 far the most common seat of the pheno- 

 menon. 



In those cases, unfortunately restricted in 

 number, in which observation has succeeded 

 in establishing the characters of blastema (as 

 in the instances of induration-blastema and 

 pus-blastema) this fluid has been found homo- 

 geneous, almost perfectly transparent, slightly 



* It is dear that what has been spoken of by 

 writers as the " conversion of blood " into the sub- 

 stance of certain Adventitious Formations can be 

 nothing more than an appearance produced by the 

 evolution of primary blastema or of absorbed blas- 

 temal elements in the interstices of a coagulum: 

 the idea of an actual change of either blood corpuscle 

 inlo the cell of an Adventitious Formation is wholly 

 inadmissible. 



